WATANABE Kiyotaka (Part-time lecturer) Professor, Kitasato University School of Veterinary Medicine After the long era of hunting and gathering, people entered the agricultural age, cultivated the land and domesticated wild animals to create a rich culture. However, people are now becoming a parasite to the earth, disturbing the balance of nature and disrupting the ecosystem. Let us study "ecology" to find out how people, the lords of creation, can successfully co-exist with the earth.